You can draw the boundary any way you want in DD.  It starts as a square, but the "shadowed" dots can be clicked and then they become new vertices allowing you to make whatever shape you want.

But be careful if you have to fly around something.  The drone will not necessarily stop at the boundary like you would.  If you have something in the middle of field on the edge you go around like a tower, the drone will continue to fly straight through.

When you look at the image on DD, you can further fine tune the boundary.